1. Field of the Invention
The present invention relates to an electrode plate of a rechargeable battery and a method for fabricating the same. In particular, the present invention relates to an electrode plate of a rechargeable battery that is capable of preventing wastage of a base film and preventing an active material layer from being irregularly formed and a method of fabricating the same.
2. Description of the Background
Recently, various portable electronic devices that are compact and lightweight such as cellular phones, notebook computers, and camcorders have been actively developed and manufactured. Such portable electronic devices are equipped with a battery pack so that a user can use the device without a separate power source. The battery pack may include at least one battery that is capable of outputting a predetermined voltage to drive the device for a predetermined period of time.
A rechargeable battery is currently provided in the battery pack for economic reasons. Rechargeable batteries include a nickel-cadmium (Ni—Cd) battery, a nickel-metal hydride (Ni-MH) battery, and a lithium rechargeable battery such as a lithium battery and a lithium-ion battery.
A lithium rechargeable battery has a drive voltage of 3.6 V or more, which is about three times higher than that of a nickel-cadmium battery or a nickel-metal hydride battery. Further, a lithium rechargeable battery has a relatively high energy density per unit mass, so it has widely been used around the world.
A lithium rechargeable battery uses lithium-based oxides as cathode active materials and carbonaceous materials as anode active materials. Generally, lithium rechargeable batteries are classified into liquid electrolyte-based batteries and polymer electrolyte-based batteries. Batteries that use a liquid electrolyte are referred to as lithium ion batteries and batteries that use a polymer electrolyte are referred to as lithium polymer batteries. In addition, the lithium rechargeable batteries are classified into cylindrical lithium rechargeable batteries, square type lithium rechargeable batteries, and pouch type lithium rechargeable batteries depending on their external appearances.
Conventionally, the lithium rechargeable battery includes an electrode assembly that has a cathode plate that is coated with cathode active materials, an anode plate that is coated with anode active materials, and a separator that is interposed between the cathode plate and the anode plate to prevent a short-circuit and to allow only lithium ions to move. In addition, the battery has a case for receiving the electrode assembly therein and an electrolyte that is injected into the case to allow the lithium ions to flow.
The cathode plate that is coated with cathode active materials and is coupled with a cathode tab is stacked on the anode plate that is coated with anode active materials and is coupled with an anode tab. Then, the separator is interposed between the cathode plate and the anode plate. The cathode plate, the anode plate, and the separator are then wound, thereby forming the electrode assembly.
The electrode assembly is housed in a battery case to prevent it from being separated from the case and the electrolyte is injected into the case. Then, the case is sealed to form the lithium rechargeable battery.
Hereinafter, a conventional method for fabricating an electrode plate of a rechargeable battery will be described with reference to FIG. 1A and FIG. 1B.
As shown in FIG. 1A, a base film 110 for a cathode current collector or an anode current collector is prepared. Cathode active materials or anode active materials are coated lengthwise along a surface of the base film 110 to form an active material layer 120. The active material layer 120 has a predetermined width W1 within a predetermined length L1 of the electrode plate and is coated over the whole area of the base film 110 except for predetermined widths W2 of the base film 110 defined at both side ends of the base film 110.
As shown in FIG. 1B, the base film 110 with the active material layer 120 is cut along the length and is then cut along the width within a length unit of the electrode plate 100 of the rechargeable battery using a cutter, thereby forming the electrode plate 100 of the rechargeable battery.
The electrode plate 100 of the rechargeable battery includes a current collector 110a and the active material layer 120 formed on the current collector 110a. In addition, both ends of the electrode plate 100 on which the active material layer 120 is not formed are referred to as uncoated portions 115.
However, in the conventional method of fabricating the electrode plate 100 of the rechargeable battery, the active material layer 120 may be formed on the whole area of the base film 110 except for predetermined widths W2 of the base film 110 that are defined at both ends of the base film 110, unnecessarily wasting the base film 110.
In addition, according to the conventional method for fabricating the electrode plate 100 of the rechargeable battery, the active materials may be coated lengthwise along the base film 110 corresponding to a length of the active material layer 120. This makes it difficult to continuously fabricate the electrode plate 100 of the rechargeable battery and increases the manufacturing time for the electrode plate 100.
FIG. 2 is a sectional view of the conventional electrode plate 100 of the rechargeable battery.
As shown in FIG. 2, the active material layer 120 formed on the base film 110 of the conventional electrode plate 100 of the rechargeable battery may have an irregular sectional shape. Since the active material layer 120 extends between uncoated portions 115 of the electrode plate 100, a front part of the active material layer 120 may be bulked and a rear part of the active material layer 120 may be attenuated. Such nonuniformities of the active material layer 120 may deteriorate the stability of the rechargeable battery including the electrode plate 100.